Understanding allogeneic stem cell transplants: What you need to know

Stem cell transplants use healthy, immature cells to replace those that either aren’t working properly in a person’s bone marrow or have been destroyed by high-dose chemotherapy. They are often used to treat leukemia, lymphoma, myeloma and other blood disorders.  

There are two types of stem cell transplants: 

• Autologous stem cell transplants use a patient’s own cells.  
• Allogeneic stem cell transplants use cells from a healthy donor. 

Why isn’t everyone a candidate to use their own stem cells? Where do donor stem cells even come from? And, why is the risk of one particular side effect greater with allogeneic stem cell transplants than with autologous transplants? 

Read on for the answers to these questions and more. 

Why isn’t everyone a candidate to use their own stem cells for a transplant? 

The type of stem cell transplant you’re eligible for depends on:  

• your type of cancer 
• whether your bone marrow is healthy and cancer-free, and  
• how your body responded to prior treatments, such as chemotherapy.  

Allogeneic transplants are the preferred type of transplant for blood cancers, such as leukemias, myelofibrosis, and sometimes lymphomas. If your bone marrow is also affected by the cancer and not healthy, we need the donor’s immune cells to react against your cancer cells.  

Autologous transplants, on the other hand, are preferred when cancer is best treated with high-dose chemotherapy. This therapy often destroys the patient’s bone marrow along with the cancer. We rebuild it by using your stem cells, which we collect beforehand.  

Where do donor stem cells come from?

Donor stem cells may come from one of three sources: 

• Blood relatives
• Unrelated adults (usually through the National Marrow Donor Program’s database)  
• Umbilical cord blood  

But the goal is to try to find a fully matched donor, whether they’re related to you or not.  

What makes someone a ‘fully matched’ donor?

A fully matched adult donor is someone whose human leukocyte antigens (HLA) are the same as yours. HLAs are two sets of proteins on the surface of our cells. We inherit them from our parents: one set from each. To be a “perfect” match, an adult donor needs to have the exact same HLA proteins as you do. Their blood type doesn’t matter. 

Umbilical cord blood, on the other hand, is still very “naïve,” in that it comes from a baby who was just born. So, its cells haven’t been exposed to all of the same bacteria, viruses, fungi, allergens and other pathogens that adult immune systems have. The cord blood’s HLA type does not need to fully match yours, though the more closely matched they are, the better.  

What are my chances of finding a fully matched adult donor?

That depends partially on the number of full siblings you have. There’s a 25% likelihood of a full match between you and each one. But the odds of you finding a fully matched unrelated donor in the national donor registry depends on your ethnicity. Here is a breakdown of those figures: 

• White or European ancestry: 74% 
• Native American or Indigenous ancestry: 47% 
• Hispanic or Latino ancestry: <40% 
• Black or African American ancestry: 19% 

It is much harder for people of color to find a perfect match. That’s why we urge members of those communities — especially younger people — to consider registering with the National Marrow Donor Program, formerly known as Be the Match.  

Are some people better candidates for allogeneic stem cell transplants than others?

Yes. But the criteria are complex. Important factors include whether your cancer is responding well to prior chemotherapy, how fit you are and the availability of a donor.  

The reason your body’s response to chemotherapy is so important is that a donor’s immune cells require several months to mount an attack against any residual cancer cells. So, if you still have too many at the time of transplant, they may overwhelm the donor’s cells and not give them a fighting chance. This could cause the transplant to fail. 

What are the benefits of an allogeneic stem cell transplant?

An allogeneic stem cell transplant is what’s known as a “high-risk/high-reward” type of therapy.  

While the risk of developing a side effect known as graft vs. host disease (GVHD) is real and significant, an allogeneic stem cell transplant is also the only potential cure for diseases like acute lymphocytic leukemia, acute myeloid leukemia, myelodysplastic syndrome, and myelofibrosis and other myeloproliferative disorders. 

GVHD is extremely rare in autologous stem cell transplants because the donor stem cells are your own. 

What are the risks of an allogeneic stem cell transplant?

The biggest risks of allogeneic stem cell transplants are infections and GVHD.  

One of the most troublesome infections is caused by a pathogen called cytomegalovirus, or CMV. Just over half of all Americans have been exposed to it by age 40. But an anti-viral drug called letermovir has been available since 2017 to prevent its reactivation after a stem cell transplant.  

GVHD is when a donor’s stem cells recognize the patient’s normal body cells as “other” and begin attacking it. We have a lot of good strategies available to prevent this, starting with finding the most well-matched donor. Another is the early use of a drug called cyclophosphamide, which targets the specific donor T cells that are more prone to reacting against the patient’s normal cells and causing GVHD.  

How long does it take to fully recover from an allogeneic stem cell transplant?

That depends on several factors:   

• How long it takes a donor’s cells to fully engraft, or establish themselves and start protecting you 
• How well you recover from the early side effects, and from GVHD, if it occurs 
• Whether other complications, such as infections, occur 
• Whether the cancer is still detectable early on, after a transplant  

But you should expect to stay in the hospital for at least 30 days after a transplant, and near the hospital for another two months. Data shows that acute GVHD or infections are most likely to happen within the first 90 days, so we want to be able to address them quickly if that happens.

Once you’ve repeated all your childhood vaccinations, your immune system should be back to normal within about two years of a stem cell transplant.

What’s the most important thing to know about allogeneic stem cell transplants?

One thing that surprises patients is how long it takes to recover. Some expect to feel normal again after just 30 days. But it can take six months or more for your energy levels, strength and even taste buds to bounce back.

Request an appointment at MD Anderson online or by call 1-877-632-6789.